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What do climate scientists think?

Filed under: — gavin @ 24 June 2010 - (Español)

by Gavin and Eric.

… and why does it matter?

There is a lot of discussion this week about a new paper in PNAS (Anderegg et al, 2010) that tries to assess the credibility of scientists who have made public declarations about policy directions. This come from a long tradition of papers (and drafts) where people have tried to assess the state of the ‘scientific consensus’ (Oreskes, Brown et al, Bray and von Storch, Doran and Zimmerman etc.). What has bedevilled all these attempts is that since it is very difficult to get scientists to respond to direct questions (response rates for surveys are pitiful), proxy data of some sort or another are often used that may or may not be useful for the specifics of the ‘consensus’ being tested (which itself is often not clearly defined). Is the test based on agreeing with every word in the IPCC report? Or just the basic science elements? Does it mean adhering to a specific policy option? Or merely stating that ‘something’ should be done about emissions? Related issues arise from mis-specified or ambiguous survey questions, and from the obvious fact that opinions about climate in general are quite varied and sometimes can’t easily be placed in neatly labelled boxes.

Given these methodological issues (and there are others), why do people bother?

The answer lies squarely in the nature of the public ‘debate’ on climate. For decades, one of the main tools in the arsenal of those seeking to prevent actions to reduce emissions has been to declare the that the science is too uncertain to justify anything. To that end, folks like Fred Singer, Art Robinson, the Cato Institute and the ‘Friends’ of Science have periodically organised letters and petitions to indicate (or imply) that ‘very important scientists’ disagree with Kyoto, or the Earth Summit or Copenhagen or the IPCC etc. These are clearly attempts at ‘arguments from authority’, and like most such attempts, are fallacious and, indeed, misleading.

They are misleading because as anyone with any familiarity with the field knows, the basic consensus is almost universally accepted. That is, the planet is warming, that human activities are contributing to the greenhouse gases in the atmosphere (chiefly, but not exclusively CO2), that these changes are playing a big role in the current warming, and thus, further increases in the levels of GHGs in the atmosphere are very likely to cause further warming which could have serious impacts. You can go to any standard meeting or workshop, browse the abstracts, look at any assessment, ask any of the National Academies etc. and receive the same answer. There are certainly disputes about more detailed or specific issues (as there is in any scientific field), and lots of research continues to improve our quantitative understanding of the system, but the basic issues (as outlined above) are very widely (though not universally) accepted.

It is in response to these attempts to portray the scientific community as fractured and in disagreement, that many people have tried to find quantitative ways to assess the degree of consensus among scientists on the science and, as with this new paper, the degree of credibility and expertise among the signers of various letters advocating policies.

It is completely legitimate to examine the credentials of people making public statements (on any side of any issue) – especially if they make a claim to scientific expertise. It does make a difference if medical advice is being given by a quack or the Surgeon General. The database that Jim Prall has assembled allows anyone to look this expertise up – and since any new source of information is useful, we think this can be generally supported. Prall’s database has a number of issues of course, most of them minor but some which might be considered more problematic: it relies on citation statistics, which have well-known problems (though mostly across fields rather than within them), it uses Google Scholar rather than the standard (ISI) citation index, and there are almost certainly some confusions between people with similar names. Different methodologies could be tried – ranking via h-index perhaps – but the as long as small differences are not blown out of proportion, the rankings he comes up with appear reasonable.

So it is now possible to estimate an expertise level associated with any of the various lists and letters that are out there. Note that it is worth distinguishing between letters that have been voluntarily signed and lists that have been gathered with nothing but political point scoring in mind (the Inhofe/Morano list was egregious in its cherry picking of quotes in order to build up its numbers and can’t be relied on as an accurate reflection of peoples opinions in any way, and similarly contributing to RealClimate is not a statement about policy preferences!). Additionally, it isn’t always clear that every signatory of each letter really believes every point in the statement. For instance, does Lindzen really believe that attribution is impossible unless current changes exceed all known natural variations (implying that nothing could be said unless we got colder than Snowball Earth or warmer than the Cretaceous or sea level rose more than 120 meters….)? We doubt it. But as tests of political preferences, these letters are probably valid indicators.

So, do the climate scientists who have publicly declared that they are ‘convinced of the evidence’ that emission policies are required have more credentials and expertise than the signers of statements declaring the opposite? Yes. That doesn’t demonstrate who’s policy prescription is correct of course, and it remains a viable (if somewhat uncommon) position to acknowledge that despite most climate scientists agreeing that there is a problem, one still might not want to do anything about emissions. Does making a list of signers of public statements, or authors of the IPCC reports, constitute a ‘delegitimization’ of their views? Not in the slightest. If someone’s views are widely discounted, it is most likely because of what they have said, not who they sign letters with.

However, any attempt to use political opinions (as opposed to scientific merit) to affect funding, influence academic hiring, launch investigations, or personally harass scientists has no place in a free society – from whichever direction that comes. In this context, we note that once the categorization goes beyond a self-declared policy position, one is on very thin ice because the danger of ‘guilt by association’. For instance, one of us (Eric) feels more strongly that some of Prall’s classifications in his dataset cross a line (for more on Eric’s view, see his comments at Dotearth).

But will this paper add much to the ‘there [is/is not] a consensus’ argument? Doubtful. People are just too fond of it.

But there really is.

427 Responses to “What do climate scientists think?”

  1. 301

    “Non-starting is the goal.”

    True, that. It’s very evident that that is precisely what is going on with many opponents of any effective mitigation policy.

    What else can explain the “anything but AGW” style of discourse, which so often leads to utter incoherence on larger scales? “It isn’t warming, but if it is then it must be the sun because Mars is warming, too. . .” etc., etc.

  2. 302
    veritas36 says:

    I prefer the term “established science” to “consensus science”: I define established science as a measurable quantity. When almost all peer-reviewed papers cease to discuss an issue, and move on to the next level of research and all significant papers on the “other side” have been refuted, the science is established.

    It’s is rare that “established science” is overturned, but it has happened. Extraordinary evidence is needed to overturn established science, although occasional anomalies may occur.

  3. 303
    Phil Scadden says:

    “What is your number ?”

    Hey its 2! (bows and crawls out backwards).

  4. 304
    Deep Climate says:

    Most of the “contrarian” letters contain a statement along the lines of “there has been no net global warming in the last x years” (where ‘x’ is some convenient cherrypicked number).

    Similarly, when one examines the papers of some of the contrarian signers, one is struck by how often the background and conclusion sections go way beyond what can be supported by the analysis (which is itself often less than compelling). Good examples would be McLean et al 2009 on ENSO, or most anything by Patrick Michaels at Climate Research.

  5. 305
    Ray Ladbury says:

    It is by no means clear what unconventional sources of fossil fuel will cost to extract once production ramps up. If you had asked petroleum geologists 20 years ago whether we’d be sucking oil through a soda straw passing through a mile of ocean and 2 miles of rock, I suspect you would have at least provided them amusement.

    Even if prices are higher, there will be 1.5 times as many people consuming energy and probably most will be living at a significantly higher standard than they are today. Again, I have zero confidence that these two crises (Peak Oil and climate change) will interfere destructively.

    WRT rising temperatures–there have been very few sustained epochs (over many decades) of warming at the paces we are now seeing. The Interglacials saw about 10 degrees warming, but it took place over a couple of millennia. We could see a comparable amount of warming in just a few centuries–the blink of an eye in geologic or paleontological terms.

  6. 306
    SecularAnimist says:

    Ray Ladbury wrote: “Even if prices are higher, there will be 1.5 times as many people consuming energy and probably most will be living at a significantly higher standard than they are today.”

    The issue with peak oil (setting aside AGW for a moment) is not whether prices are higher. It is net energy return on energy invested.

    It doesn’t just cost more petrodollars to get the “unconventional” sources — it costs more energy.

    At the point where it takes as much (or more) energy to get the fuel out of the ground and process it into usable form, then it is no longer a source of energy. It may still be a valuable commodity that people will pay a lot of money for — gold and platinum and a host of other minerals are not sources of energy either, and people pay a lot of money for them.

    But at some point, while fossil hydrocarbons will still be a valuable resource, if it takes more energy to get them into the tank or the power plant than is provided when we burn them, they will no longer be a source of energy.

    Ray Ladbury wrote: “The Interglacials saw about 10 degrees warming, but it took place over a couple of millennia. We could see a comparable amount of warming in just a few centuries …”

    Are you talking C or F?

  7. 307
    Patrick 027 says:

    “these two crises (Peak Oil and climate change) will interfere destructively”

    A potential language barrier: I presume Ray Ladbury means destroying each other, leaving a smaller net crisis. (I once read of a discussion in which one person thought the term ‘positive feedback’ in climate science meant that the feedbacks were beneficial.)

  8. 308
    Patrick 027 says:

    Re 268 Frank Giger –

    However, one must remember that many a researcher grabbed an idea and refused to let go even when the evidence went against them largely because they had defined themself as a scientist as much by their activism as their research.

    Concievable? Yes. Inevitable? No. Some people who are concerned about their reputations would prefer to correct their mistakes earlier rather than later or never. Do you have any examples in AGW? Is that what happenned with Lindzen?

    “It is quite another for a scientist to begin advocating for a specific political solution, however.”“The science is apolitical – but that stops right about the nanosecond after someone says “so what do we do about it?”

    It’s possible for politics to creep into science – (Caution: this is something I only have a vague knowledge of, but perhaps for example: early intelligence tests with racial bias – though bias in such tests can be by accident. An very interesting example is the question … I don’t remember exactly, but something like – which does not belong: potato, fork, knife, spoon, and if I remember correctly, the accepted answer today is the potato, but once upon a time it would have been the spoon (because one eats a potato with a fork and knife) – maybe it was potato, fork, plate, spoon – but you get the point; note that it is much more straightforward measuring temperature and wind then it is to measure intelligence)) – but the science tends to right itself.

    Of course, one can have ‘office politics’, and presumably that can occur at most workplaces. Politics occurs whereever people interact directly or otherwise.

    But back to your presumably intended point – once we have the science, politics comes in when it affects or potentially affects or is percieved to possibly affect anything practical or important or even philosophical/religious. But that’s the way it has to be. If there are important implications, then there are important implications. Of course the scientific knowledge – all factual knowledge, really (economics, ecology, sociology, climatology, etc.) has to be combined with a values system in order to reach a prefered plan of action.

    Politics can more narrowly apply to government, presidents and legislators, etc. It’s not necessarily bad. Often politicians use the term to refer to those unpleasant aspects (mud-slinging and evasion and misinformation) (PS I have no problem with negative campaigning in so far as the allegations are true and relevant).

    So, anyway, if you’re intending to imply that a scientist should refrain from suggesting or advocating solutions involving in part human behavior, well, if there is a problem, we can’t solve it unless there is a solution, and one way to find a solution is for someone who knows about the problem to propose or pass along a solution. Somebody has to do it if it is to be done. The politicization shouldn’t generally be declared the fault of the solution-backers.

    One can agree completely with the science and disagree with the current political solutions being offered.


    but it’s par for the course within political disagreements to lump people into boxes.


    You’ll read accusations that I’m a “denier” of the science within these comment sections for that reason – or accused of wanting to “do nothing” in the face of climate change.

    Okay, well, what is the disagreement, then? What would you rather do?

    (PS a person who is not a denier of AGW in so far as the climate change itself is concerned could still be a denier of the effects of AGW, or aspects of the potential for adaptation and/or mitigation of AGW. Of course there is room for disagreement but it is possible to step outside the boundaries of what can be substantiated, and it is possible to get known facts wrong (even if about opinions or fuzzy knowledge, one can get facts about those things wrong or ignore salient facts; one can also run into logical inconsistencies where at least one part must be wrong), and it is possible to refuse to correct one’s self over and over.)

  9. 309
    Patrick 027 says:

    Re Gilles –

    1. The scarcity of fossil fuels does limit the amount of fossil C that will be emitted (within a time frame such that they add to perturbation in atmospheric CO2 amount), but contigent on other factors, including competing energy sources.

    2. If there were no other costs to fossil fuels, then assuming an efficient market, the gradual switch from fossil fuel to alternatives and greater efficiency would procede in an optimal fashion.

    3. If there is some additional cost (AGW’s effects, ocean acification, and spills and mercury in fish, other stuff) to using fossil fuels, then the trajectory of fossil fuel use will not be optimal – it will be past optimal. The right tax would accelerate the switch to alternatives and greater efficiency in an optimal way.

    4. Of course, real markets have some inefficiencies (besides such simple (in principle) externalities.

    You had asked once before about the issue of people in the future burning the economically-recoverable fuel that we leave them as a result of such AGW policy:

    5. mass market advantage – will it still be economically recoverable if few people are using it?

    6. technology – will it still be economically recoverable given the economics of the alternatives in the future (depends on whether civilization collapses, which needn’t be from AGW – other risks are there)

    7. If it is at a sufficiently later date, then atmospheric CO2 will have dropped back. If is is released at sufficiently a slow-enough rate, it needn’t necessarily be a real problem.

    8. Who knows what people will decide to do in response to natural climate change 10,000 to millions to billions of years from now? Will we let the ice ages procede out of curiosity and for the fun of it? Will we grow fins? Will we build a giant shade in response to a brightenning sun? Will we move the Earth to a larger orbit? Will we genetically engineer plants that use TiO2 as a pigment for photosynthesis (UV-powered white plants)? Will chocolate still taste the same? – I hope so.

  10. 310
    Hank Roberts says:

    Gavin, for Gilles and others — when you refer people to AR4 WG1 Fig. 9.5, they should get a link to the page with the text of the caption explaining what those pictures mean.

    It’s a powerful image, but the text of the caption explaining the image is essential.
    Here are a few prior mentions, with bits quoted from and links to the caption text.

    (I agree with Gavin that Gilles isn’t likely to understand it, but for new readers coming along later, do look it up, you’ll be able to learn a lot from that reference)

  11. 311
    Hank Roberts says:

    PS, I’d forgotten how hard it is to find that caption for fig 9.5.
    Rather than leave the above as a scavenger hunt, here’s
    — how to find the caption,
    — the caption full text, and
    — a link:

  12. 312
    Gilles says:

    David#298 : if your simple model were really meaningful, it should be the basis of current research and well developed in IPCC reports. Is it the case and where ? If not, do you consider that IPCC has missed a simple and efficient way of proving the effect of GHG ?

    SecularAnimist#299 “Dangerous global warming is occurring NOW, the result of the fossil fuels that we have already burned.”

    I’m perplex : if you can’t define a significantly “more dangerous” level, above some integrated amount of burned FF, what’s the point of trying to reduce them ? if it’s all already done, let’s finish the rest and prepare to the consequences that will happen whatever we do.

    #306 Ray
    actually forecasts of oil production have been rather over-optimistic these last years, so I think people thought more things would be possible in the future, than what actually happened.

    “Even if prices are higher, there will be 1.5 times as many people consuming energy and probably most will be living at a significantly higher standard than they are today.”

    May be, but then why would a tax change this situation ?

    “WRT rising temperatures–there have been very few sustained epochs (over many decades) of warming at the paces we are now seeing. ”

    This sentence is kind of an answer to my question : “very few”, statistically speaking, really means that the current slope should be outside by more than one sigma from the central value of comparable epochs on the same time interval (or equivalently that the amplitude of the Fourier component at T^-1 exceeds by a lot the natural PSD at this frequency).

    This may be true again – but my only question is : where is the scientific evidence proving that ? if you can’t answer this very basic question, you can’t be surprised that some people emit doubts about it.

  13. 313
    Gilles says:

    [edit – one-a-day remember?]

  14. 314
    Gilles says:

    Hank : I don’t think I misunderstand Fig 9.5, which really deals with attribution in the sense I recalled : assuming we understand well enough the background “noise” (which would be rather a “known signal” in this case ), to substract it and evaluate correctly the anthropogenic residual. Of course this is perfectly arguable – the only thing is that it is much less comfortable than the case when the signal clearly emerges (at a several , say 5 sigma level) from a unknown noise, because in this case you don’t have really to justify that you understand very well the noise – actually you don’t care at all about it.

    In the opposite case, you have to convince people that you REALLY understand very well the noise. And that can be a little bit .. tricky. Shall I consider that you’re likely to understand what I’m saying ?

    [Response: Sigh…. you are talking about attribution, and we discussed that all last month. Please read that discussion again before repeating things that are irrelevant to the situation we actually have. – gavin]

  15. 315
    Didactylos says:

    Gilles, you are asking the wrong question. Until you understand enough to ask the right questions, you will remain firmly at sea.

    When you are asking the wrong questions, you get answers that don’t help you.

    I think perhaps you need to be a little less credulous when accepting things coming from some of the other sources you seem to be reading. (5 sigma? That nonsense has Motl’s fingerprints all over it.) Try to apply the same level of scepticism to everything you read, not just to people with whom you disagree.

  16. 316
    SecularAnimist says:

    Gilles wrote: “if it’s all already done, let’s finish the rest and prepare to the consequences that will happen whatever we do.”

    Thank you for reminding me, with that bit of drivel, just exactly why discussions with you are a foolish waste of time.

  17. 317
    Gilles says:

    Didactylos : saying that asking about the significance of a variation is a “wrong question” sounds rather strangely for a scientist. FYI : I don’t know the works and writings of Mr Motl. 5 sigmas is the standard requirement of the international experimental collaboration I’m belonging to, before claiming a detection. I wouldn’t dare argue that it is nonsense before them, but I can invite you to do so it if you want.

  18. 318
    Gilles says:

    317 : Secular animist : there wasn’t any irony in my answer. Do you think there is a reachable threshold it is worth keeping below , and if yes, which one, and how much GtC would produce it ? it’s unclear after what you said !

  19. 319
    MartinJB says:


    you keep asking why a tax would make a difference in fossil fuel consumption. I understand why you ask the question. After all, assuming substantial use of unconventional fossil fuels (UFFs) in the BAU scenario, suggests a certain amount of insensitivity to price (assuming UFFs are significantly more expensive than conventional fossil fuels).

    My first thought is that adding the cost of a carbon tax to the already higher cost of UFFs will make less carbon-intensive energy sources that much more attractive, encouraging more switching to alternative energy sources. The higher the tax, the larger that incentive. What’s more, if we actually use proceeds of the carbon tax to subsidize R&D and implementation of low-carbon alternatives, we get a multiplier effect.

    More importantly, I think most people who are adequately concerned about combating climate change prefer a cap-and-trade system anyway. A carbon tax is, IMHO, not up to the task. We have a lot less ability to determine the correct tax to bring about the desired decrease in demand than we have the ability to determine how much more carbon we can add to the atmosphere. So, set the cap (akin to there being limited amounts of a resource), and let markets determine the price. It’s the amount of CO2e, not the price that’s really important.


  20. 320
    Didactylos says:

    Oh, Gilles, Gilles, Gilles.

    Why do we waste our time? You are clearly not posting in good faith. As such, you don’t deserve any answers.

  21. 321
    Ray Ladbury says:

    Gilles asks, “May be, but then why would a tax change this situation ?”

    A tax on a particular energy source makes other sources more attractive. It may also spur innovation as inventive minds try to figure out ways to decrease costs. If you change the incentives, you may redirect peoples efforts away from finding ever cheaper ways of digging up the entire Orinoco basis and toward developing a sustainable energy infrastructure. You also may cause fossil fuels to better reflect their true cost, including environmental degradation.

    As opposed to now, where we have 1)fossil fuels directly subsidized by government tax and land use regulations; 2)driving foreign and military policy of the entire industrialized world. I would like nothing better than to be able to tell the Oil barons they can keep their oil-filled sandboxes.

  22. 322
    Hank Roberts says:

    Gilles, above:
    > when the signal clearly emerges (at a several , say 5 sigma level)
    > from a unknown noise,… you don’t have really to justify that you
    > understand very well the noise ….

    Climatologists don’t ignore natural “noise” — look at a big signal in the paleo record; natural forcings explain it. Understanding the “noise” is basic to understanding the anthropogenic signal.

    Kick-starting ancient warming
    E. G. Nisbet et al., Nature Geoscience 2, 156 – 159 (2009)
    “… we are concerned only with the event that triggered the PETM. No attempt is made to model the entire climate behaviour over the PETM itself…. such a triggering warming occurs over decades to centuries …. we start by defining specific geological processes that can release greenhouse gases.”

    Tamino, at wrote:

    “There’s nothing wrong with 5-sigma, we’d all love to have it all the time, but *requiring* it is indeed ludicrous…. a 5-sigma standard ignores *most* of what can be learned…. the suggestion that results which don’t reach 5 sigma should be discounted is nothing but a recipe for missing out on a lot of good science…. Sometimes it’s downright impossible — how many times should we repeat the global-warming experiment?”

  23. 323
    Geoff Wexler says:

    # 318

    5 sigmas is the standard requirement..

    for X, and 2 sigmas may be more suitable for lots of different Y’s.

    What’s X by the way?

    If you were warned not to drive your car home, would you ignore the advice unless it came with a 99.999% (or whatever) probability that a wheel would fall off in the next 10 miles?.

  24. 324
    Geoff Wexler says:

    To demangle my previous remark.

    The quote ends after the first line.
    My comment on it begins on the 2nd. line

  25. 325
    Doug Bostrom says:

    FoGT examines Jim “Torquemada” Prall, suggesting that nobody signing an petition ever expected the Spanish Inquisition: Global Inquisition into Spanish Warming

  26. 326
    David B. Benson says:

    Gilles (313) — I could not of developed such a simple model without using information in the IPCC AR4 WG1 report and rathr more as well; see the notes in that link. Later I learned of the existence of Tol, R.S.J. and A.F. de Vos (1998), ‘A Bayesian Statistical Analysis of the Enhanced Greenhouse Effect’, Climatic Change, 38, 87-112, which does much the same, more thoroughly, but didn’t include the AMO as an index of intrnal variability.

    Such a simple model is not an attribution sudy; there are plenty of those. For example, Hegerel et al. (2006) was of particular interest to me. I left out the possiblity of a linear trend, due to whatever. If included, the best fitting trend is 0.063 K/century. Orbital forcing? Sun? In any case, simply overwhelmed by the CO2 induced warming.

    The point for such a simple model is that it should be accessible to most as a starting point, readily duplicatable on one’s own, to provide an approximate understanding of the instrumental record. Notice I also made an actual prediction in the linke comment.

  27. 327
    John E. Pearson says:

    320: MartinJB said: “I think most people who are adequately concerned about combating climate change prefer a cap-and-trade system [to a carbon tax] anyway.”

    Neither Jim Hansen nor my young friend who just graduated w/ honors from Berkeley with an economics degree prefer cap-and-trade to a carbon tax. I tend to listen to them but you’re welcome to try to convince me why cap-and-trade is superior to a carbon tax.

  28. 328
    Hank Roberts says:

    leads to a variety of sources that might come from whatever physics program Gilles is involved in.

    This for example is helpful:

    “Posted by Zachary Marshall on 10 Apr 2010 at 02:11 pm

    Physicists try to be very clear about what they say (believe it or not!). If we claim to have “discovered” something, then millions, or even billions, of dollars could be put towards studying it. We’d better be sure!

    Here are a couple of nice pictures we can talk about. Both are taken from the Particle Data Group…. And both of these are measurements as they have evolved with time…. it looks like the first measurements of the neutron lifetime were way off! And, contrarily, it looks like the W-boson mass measurements might even be too good! Either way, it is satisfying to see error bars on all these measurements. That part is really important! It allows the possibility that you’re wrong.

    … When ever we physicists claim to discover a new particle, for example, we require that it be outside the expected error bar by at least five times the error bar’s width (called five standard deviations or five “sigma” …. Three sigma is often called “observation,” two sigma is often called “evidence.” And we usually choose to consider something new “excluded” if it is ruled out by three sigma….

    This sounds complicated, but it’s all to ensure that we are very confident about what we’ve seen before announcing to the world that we have discovered a new particle! If you trust your error bars completely, five sigma means the chance we’re wrong is 0.00006%!! And this is also what we spend a huge amount of our time on: making sure those error bars are honest!

    Next time I’ll talk a bit about what happens if we’re wrong!…”


  29. 329
    MartinJB says:

    Well, Mr. Pearson, I wasn’t trying to convince you. I was really just expressing my observation of what people think about how to combat global warming. Regardless, my rationale is pretty simple. Cap and trade provides a direct signal to markets: This is how much CO2e you have to play with. With a carbon tax, you set it and hope it has the desired impact on demand. Obviously, one can adjust, but sacrifices predictability.

    There are a lot of details and caveats I gloss over, but the broad principal is, I think, pretty robust.

    Now, I know nothing about your friend except that he has a possibly relevant degree from Berkeley. Hansen is a terrific scientist, but I don’t know about his background in markets and resource economics. What are their rationales for their opinions? That might be a better place to start than just taking their word for it. Your call.

    But this is really a distraction. The post was about Gilles’s sorta straw-man.


  30. 330
    Patrick 027 says:

    Re 330 MartinJB

    The principle of a tax can be based on the net public cost. This is of course not a simple matter to compute, but for the same reason, it is not a simple matter to compute what level a cap should be set at. Ideally, The cap should be set so that the market produces the same price signal that the tax would impose, while the tax would keep emissions at the level of what would be the cap.

    A nonlinearity in principle can be dealt with by simulating the trajectory of total value (the value that we want to optimize) and finding the tax that produces the greatest values.

    The cap becomes more obviously preferable if the public cost per unit emission sharply increases beyond that point.

    A cap is predictable for emissions and potentially unpredictable for price signal. A tax is predictable for price signal and potentially unpredictable for emissions. However, a tax can be started low (which we’d want to do anyway so as to not shock the economy) and ramped up, and adjusted as necessary. The emissions in one particular year can be higher or lower without much difference in effect if combined with a complemetary shift in another year; a tax allows such flexibility; maybe caps do as well but I’m not sure. Caps have to be auctioned (ideally) or else given away. On the other hand, perhaps caps are more amenable to international trade? But a tax can come with tariffs/subsidies on imports/exports to balance differing national policies.

  31. 331
    Patrick 027 says:

    …it is not a simple matter to compute what level a cap should be set at. – oh, well, maybe simpler, but …

  32. 332
    Gilles says:

    321 Dydactylos : this, at least, is totally wrong.

    Let me state as clearly as possible that I’m posting here in a total good faith – I may be wrong , like anybody, but I expose as clearly as possible all the problems and the contradictions I can see in many speeches about GW. I do it because I can’t understand them, and only because that – for the simple reason that I am not involved in any party , I have absolutely no financial (despite what some of you apparently believed) and even no scientific involvement in any climate or energy issue. I am only a scientist and a citizen, and I try to apply my scientific understanding to a citizen problem. I agree that many of the issues I’d like to discuss do not imply directly climate science and should perhaps be discussed elsewhere, such as the amount of FF reserves, the effect of a tax, the discussion about the benefit-cost of fossils and so on, but they are nevertheless important in the debate, and many of you seem to have also some ideas about them.

    So hearing here digressive comments about the number of posts, my bad or good faith, my intellectual qualities, my capacities of listening or understanding, and whether my questions are “right ” or “wrong” really don’t help me much. I think at 48 that I know pretty well who I am, thanks for trying to help me but I don’t really need your help. If my questions are wrong, please tell me WHY and not just “you’re wrong”.

  33. 333
    Gilles says:

    327 : David Benson : So what is the central value and the dispersion of the average slope in the previous centuries ? I guess that the central value is pretty close to zero, but that is the standard deviation ? Is it really something like 0.15 or 0.2 K/ century or smaller , or not ? where is the scientific assessment of this dispersion ? already since the current value is estimated by modern thermometers and a world wide grid that weren’t available in the past times, a precise determination of this dispersion is obviously a tough task.

    The other answers do address a different problem : They don’t answer the question of whether we HAVE a 3 or 5 sigma signal, but rather whether we NEED such a signal before acting. Obviously this is a different issue – it doesn’t belong strictly speaking to the field of climate science, and I don’t how much we are allowed to elaborate on this here (the exact border of what is on and off topics on RC is still slightly unclear for me) .

    But it some sense , it is a confirmation of what I said ; arguing that we don’t NEED it only makes sense if we don’t HAVE it – of course if we had it , as I said, the issue would be much simpler.

  34. 334
    Gilles says:

    GW : it all depends on benefits and costs. In you example, of course I will repair my wheel, because the cost of doing it is incomparably smaller. Now if a country was told that there is a 99.999 % chance that there will be more than 30 000 casualties in car crashes for the coming year, with a cost larger than 100 billions of $ , would it ban the use of cars? the answer is no of course, because actually US know it, and don’t ban cars. But this is not climate science.

  35. 335

    HotRod #243: it’s not a false dichotomy. There was an active and vocal AIDS denial movement that according to one estimate caused over 300,000 unnecessary deaths in South Africa.

  36. 336

    Gilles, 5 sigma is a reasonable standard if you are doing a huge number of measurements to detect an unlikely event. For example, if you do a billion measurements, observing an event once that has p=1E-9 is not surprising.

    That is not the scenario we are dealing with here.

  37. 337
    Gilles says:

    334 : Philip : it is by no mean necessary to make a huge number of measurements before observing a 5 sigma event, because the “sigma” is evaluated with the noise WITHOUT the external cause that superimposes to the noise. You routinely detect much above 5 sigmas when you read any text or listen to any conversation. The point is here to detect something that is supposed to have significantly changed with respect to a former situation.

  38. 338
    John E. Pearson says:

    330: MartinJB said: about cap and trade versus taxes:

    I’ll try to understand Hansen’s rationale well enough to explain it over the next day or so, and perhaps my economist friend’s as well. Hansen walked through these arguments in “Storms of My Grandchildren”.

    My friend said that taxes are more efficient. Among Hansen’s arguments were that cap and trade removes incentive for individuals to reduce their CO2 emissions since it just gives someone else the right to emit more.

    330: MArtinJB said: “this is really a distraction. The post was about Gilles’s sorta straw-man.”

    Actually Gilles’ straw-men are the distraction. Effective policy is far important than arguing over nonsensical straw-men. I don’t think Krugman particularly agrees or disagrees with advantages of cap & trade versus a tax:

  39. 339
    Hank Roberts says:

    > You routinely detect much above 5 sigmas when you read any text

    Not yours, sorry. All I detect is “anything but the IPCC” noise.

  40. 340
    Brian Dodge says:

    Regarding modern versus past rate of temperature increase – I downloaded data from NOAA’s National Climatic Data Center[1] and calculated the change in temperature versus time interval(s). No annual rate of change in either dataset exceeded the 0.0075 degree per year change in HadCRUTv3[2]. Because of limitations in Appleworks, the ranges only covered ~100k 0r 240k years,or 480+ datapoints, depending on the dataset. There were less than ten datapoints in either dataset (<3%) that exceeded HALF the rate of change that we have measured in the last century.

    In other news, has announced "Northwest India may have to wait beyond July 6 to see the onset of monsoon rains, according to latest updates by international models. The US National Centres for Environmental Prediction (NCEP) is of the view that entire Rajasthan, parts of west Madhya Pradesh, Punjab, Himachal Pradesh, Uttarkhand and Jammu and Kashmir may be denied timely onset of the rains."

    The d18O data(first URL) is sampled at 500 year intervals, and the derived temperature data(second URL) is at 250 year intervals.

  41. 341
    Bill says:

    Warmest June in the Central England Temp record was 1846. Data just released …..dont panic !

  42. 342
    Ray Ladbury says:

    Gilles says: “it is by no mean necessary to make a huge number of measurements before observing a 5 sigma event, because the “sigma” is evaluated with the noise WITHOUT the external cause that superimposes to the noise.”

    Gilles, come on. You can’t be that ignorant of statistics! Think about what you write before you write it.

    Bill@342 That might be a comfort if the entire world were bounded by Central England. Last I saw, it was not. Maybe go check a map.

  43. 343
    Bill says:

    or you look at at a good longterm temp record

  44. 344
    Ray Ladbury says:

    Bill@344, and that, too, might be a comfort if we had a complex civilization that had survived the PETM. I know of none. You?

  45. 345
    Bill says:

    Many mid-USA temp data sets show the same picture as the CET .for example :

  46. 346
    David B. Benson says:

    Gilles (327) — You could try looking at the almost two dozen “hockey stick” papers. MOre simply, and longer ago, the great (6 K) change during the transition from LGM to Holocene took about 60 centuries; an average of 0.1 K/century during a time of dramatic change in comparison to most of the prior 115,000 years.

  47. 347
    David B. Benson says:

    Human-Made Global Warming Started With Ancient Hunters

  48. 348
    Gilles says:

    Hank, Ray : Take a single picture of a star with a telescope, evaluate the background around it by measuring the number of photons in similar apertures on the “black” sky, and the associated statistical photon noise, and you very easily have a 5 sigma signal. You don’t even need a lot of photons, some high energy observations with very low backgrounds can detect a significant signal with one single photon !

    David : I read some hockey stick papers, and I didn’t find where the slope measured in a homogeneous way by the proxies exceeds the natural noise. What exceed the natural noise are the instrumental temperatures, but you don’t really know what they would have been in the past since they simply don’t exist before the time they are supposed to grow. So contrary to the picture of the star, you don’t have a proper “black sky” to calibrate the noise.

    The answer about LGM/holocene transition is not relevant because you sample the variability on different timescales, whereas my question was about the statistical noise AT THE SAME TIMESCALE. in other words , you compare different frequencies of the power spectral distribution. This is by no ways innocent : the SLOPE of the temperature rise from 6 am to 12 am of a summer day is much, much greater than any slope you will measure at the year scale or the century scale … but nobody worries about it of course.

  49. 349
    Ray Ladbury says:

    Gilles says, “Take a single picture of a star with a telescope, evaluate the background around it by measuring the number of photons in similar apertures on the “black” sky, and the associated statistical photon noise, and you very easily have a 5 sigma signal.”

    Great, Gilles, now go publish a paper based on this 5 sigma signal. The question is not whether you can engineer a 5-sigma signal, but rather what is necessary for confidence in a result. Two sigma will do in most cases, and 3 you can take to the bank. OTOH, I saw six-sigma signals from particle physics experiments that were absolutely beautiful, but had the wrong sign of particles. You concentrate way too much on numbers and too little on how those numbers are determined.

    [edit – stay substantive please]

  50. 350
    Geoff Wexler says:

    Re #335

    Now if a country was told that there is a 99.999 % chance that there will be more than 30 000 casualties in car crashes for the coming year, with a cost larger than 100 billions of $ , would it ban the use of cars? the answer is no

    Apart from distorting my analogy, you have shifted your ground. Your example illustrates a case for which 100% (as good as makes no difference) certainty would be insuffient. Why point this out?

    It suggests that lack of certainty (number of sigmas) is not your real concern. If the certainty were to rise, you would be ready with the money issue.